1. Field of Invention
This invention relates to water streams containing odorous species and, in particular, to controlling dissolved sulfide concentrations by using a dose to demand model based on an oxidation reduction potential of the water stream to vary a feed rate of a salt introduced to the water stream.
2. Discussion of Related Art
It is known to add nitrates or nitrites, and/or anthraquinone, to sewage to suppress the formation of dissolved sulfides via anaerobic bacterial action. For example, Howe et al., in U.S. Pat. No. 3,300,404, disclose anaerobic treatment of organic industrial wastes in an artificial lagoon; List, in U.S. Pat. No. 4,446,031, discloses sewage treatment composition, its manufacture, and its use; Mouché et al., in U.S. Pat. No. 4,681,687, disclose the use of alkali metal nitrates to inhibit H2S formation in flue gas desulfurization system sludges; and Tatnall, in U.S. Pat. No. 5,500,368, discloses finely divided anthraquinone formulations as inhibitors of sulfide production from sulfate-reducing bacteria, the entire content of each being expressly incorporated hereinto by reference. Further, Ballinger, Jr. et al., in U.S. Pat. No. 6,309,597, disclose a method for reducing hydrogen sulfide level in water containing sulfate-reducing bacteria and hydrogen sulfide-metabolizing bacteria. Bowers, in U.S. Pat. No. 5,045,213, discloses a waste water treatment method and apparatus. Richards, in U.S. Pat. Nos. 5,200,092 and 5,336,431, discloses a composition and method for sulfide control. Miklos, in U.S. Pat. No. 6,660,163, discloses waste treatment with control over biological solids. Vineyard, in U.S. Pat. No. 6,576,144, discloses a method and apparatus for pretreatment of wastewater streams by chemical oxidation.
Recently, it has been proposed via commonly owned U.S. Pat. No. Re. 37,181 and Re. 36,651 (the entire content of each is expressly incorporated hereinto by reference) that the addition of nitrate, typically via an aqueous nitrate salt solution, to sewage systems, waste treatment plants and other industrial waste applications containing dissolved sulfides will result in the elimination or substantial reduction of the sulfides, as well as the elimination of other minor odors associated with other sulfur-containing compounds. It is also known that significantly raising the pH of water streams (i.e., to greater than 10) by addition of an alkaline material (i.e. sodium hydroxide, calcium hydroxide) causes significant reduction of biological activity that produces dissolved sulfide.
Unfortunately, this significant pH increase of wastewater can adversely affect operation of wastewater treatment plants. Alkali addition also causes a shift in the dissolved sulfide equilibrium, so that more of the volatile dissolved hydrogen sulfide (H2S) is converted into nonvolatile sulfide ion (S2−), thereby preventing release of hydrogen sulfide gas. However, hydrogen sulfide can still be stripped downstream (i.e. released to the atmosphere) as untreated additional flows become mixed with the alkaline treated wastewater, thereby reducing its pH, and nonvolatile sulfide ion is converted back to volatile dissolved hydrogen sulfide. As a result, operating a wastewater system at such a high pH level does not typically allow for satisfactory odor control on a continuous basis.